The present invention relates to a hydraulic machine. More particularly, this invention concerns a gear-type hydraulic pump or motor.
A hydraulic machine is known wherein two meshing gears have parallel axis-defining shafts received in respective journals in turn having end faces turned axially toward the respective gears. These journals are formed at their end faces with cutouts opening in opposite directions in line with input and output passages formed in a housing carrying the journals and enclosing the gears.
Usually in such a machine the journals are basically cylindrical, and each abuts the other at a plane that extends parallel to the respective journal axis. In this manner rotation of the journals about their axes is prevented. In such an arrangement one or both of the gears can be driven in order to operate the device as a pump, or pressurized fluid can be forced through it to use it as a hydraulic motor.
The cutouts formed at the axial ends of the journals facing the gears are usually each constituted in half by one of the journals and have outwardly open generally rectangular shape. These cutouts ensure proper flow of fluid into the spaces between the gear teeth and maximize efficiency in operation of the pump or motor. A disadvantage of such a formation is that it decreases the size of the abutting and, hence, sealing surfaces of the adjacent bearings so that leakage between the journals becomes possible. Furthermore, the fluid is channeled by such formations to the teeth in such a manner as often to cause premature wear of these teeth and leakage through the pump or motor. The two journals form a relatively thin wall between the inlet or low-pressure side of the device and outlet or high-pressure side.